Cobalt-iron double-active-site synergistic catalyst, preparation method thereof and application of cobalt-iron double-active-site synergistic catalyst in carbonate pyrolysis CO2 coupling ethane oxidative dehydrogenation

Abstract

The invention discloses a cobalt-iron double-active-site synergistic catalyst, a preparation method thereof and application of the cobalt-iron double-active-site synergistic catalyst in carbonate pyrolysis CO2 coupling ethane oxidative dehydrogenation. The cobalt-iron double-active-site synergistic catalyst is obtained by adopting a soluble metal salt mixed solution and an alkaline solution through nucleation stirring, crystallization and high-temperature roasting. The catalyst prepared by the invention has excellent catalytic activity, selectivity and thermal stability, realizes efficient preparation of C2H4 and CO, simultaneously realizes full utilization of waste heat in the carbonate pyrolysis process and resource conversion of CO2, and contributes to promotion of development of environment-friendly society and circular economy.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst preparation, and specifically relates to a cobalt-iron dual-active-site synergistic catalyst and a preparation method thereof, and application thereof in carbonate pyrolysis CO2 coupled ethane oxidative dehydrogenation. Background Art

[0002] Metal oxides produced by carbonate pyrolysis are important raw materials in process industries such as cement, steel, and refractory materials. However, carbonate decomposes to form metal oxides at high temperatures, but also produces and releases a large amount of CO2. According to statistics, more than 50% of industrial carbon emissions in the country come from high-temperature pyrolysis of carbonate. Therefore, it is crucial to significantly reduce CO2 emissions while effectively utilizing carbonate resources.

[0003] CO2-ODHE is an effective method for converting greenhouse gases CO2 and C2H6 into C2H4 and CO. C2H4 is the basic organic raw material for the production of chemicals such as styrene, ethylene oxide, and vinyl chloride, and is the core of the petrochemical industry. CO is used for downstream reactions, and a series of platform chemicals can be synthesized through existing mature processes such as Fischer-Tropsch synthesis and methanol synthesis. However, the industrial application of CO2-ODHE technology is limited by the catalyst's easy carbon deposition and deactivation at high temperatures and the low CO2 conversion rate.

[0004] So far, CO2-ODHE has been widely studied, among which precious metal catalysts have high activity, but their high cost limits their large-scale application. In contrast, non-precious metal catalysts, especially cobalt-based catalysts, are widely used in the dehydrogenation of light alkanes due to their low price and selective destruction of CH bonds. However, the conversion rate of CO2-ODHE reaction is very low, and it is still a challenge to adjust the catalytic performance of cobalt catalysts and controllable product selectivity. Summary of the invention

[0005] The present invention is proposed to overcome the shortcomings of the prior art, and its purpose is to provide a cobalt-iron dual-active site synergistic catalyst and a preparation method thereof and application in carbonate pyrolysis CO2 coupled ethane oxidative dehydrogenation.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing a cobalt-iron dual-active-site synergistic catalyst comprises the following steps:

[0008] (i) preparing a soluble metal salt mixed solution;

[0009] (ii) preparing an alkaline solution;

[0010] (iii) adding a soluble metal salt mixed solution and an alkaline solution into a nucleation reactor, and stirring the mixture to obtain a primary product;

[0011] (iv) The initial product is placed in a reaction vessel for crystallization, and the crystallized product is washed, dried, and ground to obtain a cobalt-iron dual-active site synergistic catalyst precursor (Co x Mg3Al2Fe y -LDHs);

[0012] (v) calcining the cobalt-iron dual-active-site synergistic catalyst precursor at high temperature to obtain the cobalt-iron dual-active-site synergistic catalyst (Co x Mg3Al2Fe y -MMO).

[0013] In the above technical solution, the solute of the soluble metal salt mixed solution includes soluble cobalt salt, soluble magnesium salt, soluble iron salt and soluble aluminum salt; the solvent of the soluble metal salt mixed solution is deionized water.

[0014] In the above technical solution, ultrasonic dispersion is adopted for 5 minutes to 30 minutes when preparing the soluble metal salt mixed solution and the alkaline solution.

[0015] In the above technical solution, the soluble cobalt salt is cobalt nitrate or cobalt chloride; the soluble magnesium salt is magnesium nitrate or magnesium chloride; the soluble iron salt is iron nitrate or iron chloride; and the soluble aluminum salt is aluminum nitrate or aluminum chloride.

[0016] In the above technical solution, the molar ratio of the soluble cobalt salt, the soluble magnesium salt, the soluble aluminum salt and the soluble iron salt is (0.5-2):3:2:(0.1-0.5).

[0017] In the above technical solution, the solute of the alkaline solution includes sodium hydroxide and sodium carbonate, and the solvent of the alkaline solution is deionized water.

[0018] In the above technical solution, the molar amount of the sodium carbonate is 2 times the total molar amount of trivalent cations in the soluble metal salt mixed solution; the molar amount of the sodium hydroxide is 1.6 times the total molar amount of cations in the soluble metal salt mixed solution.

[0019] In the above technical scheme, the rotation speed of the nucleation stirring in step (iii) is 3000 rpm, and the stirring time is 5 minutes; the crystallization conditions in step (iv) are crystallization at 120°C for 24 hours; and the high-temperature calcination conditions in step (v) are calcination at 800°C for 4 hours in an air atmosphere.

[0020] A cobalt-iron dual-active site synergistic catalyst, the catalyst is Co1Mg3Al2-MMO, Co1Mg3Al2Fe 0.1 -MMO, Co1Mg3Al2Fe 0.2 -MMO or Co1Mg3Al2Fe 0.5-MMO.

[0021] Application of a cobalt-iron dual-active-site synergistic catalyst in carbonate pyrolysis CO2 coupled ethane oxidative dehydrogenation. The reaction conditions of carbonate pyrolysis CO2 coupled ethane oxidative dehydrogenation are as follows: under normal pressure, a cobalt-iron dual-active-site synergistic catalyst is filled in a continuous fixed bed reactor, and a mixed gas of ethane and carbon dioxide is introduced for reaction, wherein the reaction gas is 5% CO2+5% C2H6+Ar, the reaction temperature is 600°C-700°C, and the space velocity is 9000ml·g -1 ·h -1 .

[0022] The beneficial effects of the present invention are:

[0023] The present invention provides a cobalt-iron dual-active-site synergistic catalyst and a preparation method thereof and application in carbonate pyrolysis CO2 coupling ethane oxidative dehydrogenation. The cobalt-iron dual-active-site synergistic catalyst prepared by the present invention is used to achieve the effect of synergistic catalysis by regulating the contents of Co and Fe on a MgAl2O4 spinel carrier. Co selectively breaks the CH bond and is the main active site for promoting ethane dehydrogenation, while the Fe site is responsible for the dissociation of carbon dioxide and supplements lattice oxygen to enhance ethane oxidative dehydrogenation. Based on this, it is applied in the CO2-ODHE reaction to show good catalytic performance. At 675°C, the conversion rate of ethane can reach 18.2%, the ethylene selectivity exceeds 90%, and the catalyst stability is good in the reaction. Compared with the catalysts in the prior art, the CO2-ODHE catalyst provided by the present invention has strong high-temperature stability, a simple preparation method, and the advantages of low production cost. The carbonate pyrolysis CO2 and ethane dehydrogenation reaction processes are co-thermally coupled and occur in the same catalytic system, which can reduce energy consumption and production costs. The present invention fully utilizes the high-temperature waste heat generated by carbonate pyrolysis, while promoting the secondary utilization of carbon sources in carbonates, effectively reducing CO2 emissions, promoting the efficient production of ethylene and CO, and opening up a new path for carbon circulation and sustainable utilization of resources, with significant environmental and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 is a scanning electron microscope photograph of the cobalt-iron dual-active-site synergistic catalyst prepared in Example 1 of the present invention;

[0025] Figure 2 is a projection electron microscope photograph of the cobalt-iron dual-active-site synergistic catalyst prepared in Example 1 of the present invention;

[0026] Figure 3 This is a stable performance diagram of the cobalt-iron dual-active-site synergistic catalyst prepared in Example 1 of the present invention.

[0027] Figure 4It is a comparison chart of the application performance of the catalyst prepared in Example 1 of the present invention and other catalysts.

[0028] Figure 5 It is a performance comparison chart of the catalysts prepared in Examples 1 to 4 of the present invention.

[0029] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0030] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0031] Example 1

[0032] A cobalt-iron dual-active-site synergistic catalyst (Co1Mg3Al2Fe 0.2 -MMO) preparation method, the specific steps are as follows:

[0033] First, a mixed solution of 0.01 mol / L cobalt nitrate, 0.01 mol / L magnesium nitrate, 0.01 mol / L iron nitrate and 0.01 mol / L aluminum nitrate was prepared with deionized water, and a mixed solution of 1.6 times the total molar amount of cations in sodium hydroxide and 2 times the molar amount of trivalent cations in sodium carbonate was prepared with deionized water; the two mixed solutions were transferred to a nucleation reactor and stirred for 5 min; the mixed solution was charged into a reactor and crystallized at 120 ° C for 24 h to obtain Co1Mg3Al2Fe 0.2 -LDH catalyst precursor; the obtained product was washed, dried, ground, and then heated to 800°C at 5°C / min in a muffle furnace, calcined for 4 hours, and then cooled to room temperature at 10°C / min. Carbon dioxide oxidation ethane dehydrogenation reaction Weigh 0.1g of catalyst for reaction.

[0034] The Co1Mg3Al2Fe 0.2 -SEM image of MMO catalyst is attached Figure 1 ,from Figure 1 It can be seen that the hydrotalcite nanosheet morphology exists stably; Figure 2 The Co1Mg3Al2Fe 0.2 -HRTEM image of MMO catalyst, Figure 3 It shows that Co1Mg3Al2Fe 0.2 -MMO catalyst at space velocity 9000ml g -1 ·h -1 Under the condition of high temperature, it has good catalytic activity and stability; Figure 4 It shows that the Co1Mg3Al2Fe 0.2-MMO catalyst has higher ethane conversion rate and ethylene selectivity than other catalysts.

[0035] Example 2

[0036] A method for preparing a cobalt-iron dual-active-site synergistic catalyst (Co1Mg3Al2-MMO), the specific steps are as follows:

[0037] First, a mixed solution of 0.01 mol / L cobalt nitrate, 0.01 mol / L magnesium nitrate and 0.01 mol / L aluminum nitrate was prepared with deionized water, and a mixed solution of 1.6 times the total molar amount of cations of sodium hydroxide and 2 times the molar amount of trivalent cations of sodium carbonate was prepared with deionized water; the two mixed solutions were transferred to a nucleation reactor and stirred for 5 minutes; the mixed solution was loaded into a reactor and crystallized at 120°C for 24 hours to obtain a Co1Mg3Al2-LDH catalyst precursor; the obtained product was washed, dried and ground, and then heated to 800°C at 5°C / min in a muffle furnace, calcined for 4 hours and then cooled to room temperature at 10°C / min. Carbon dioxide oxidation ethane dehydrogenation reaction Weigh 0.1g of catalyst for reaction.

[0038] Example 3

[0039] A cobalt-iron dual-active-site synergistic catalyst (Co1Mg3Al2Fe 0.1 -MMO) preparation method, the specific steps are as follows:

[0040] First, a mixed solution of 0.01 mol / L cobalt nitrate, 0.01 mol / L magnesium nitrate, 0.01 mol / L iron nitrate and 0.01 mol / L aluminum nitrate was prepared with deionized water, and a mixed solution of 1.6 times the total molar amount of cations in sodium hydroxide and 2 times the molar amount of trivalent cations in sodium carbonate was prepared with deionized water; the two mixed solutions were transferred to a nucleation reactor and stirred for 5 minutes; the mixed solution was charged into a reactor and crystallized at 120°C for 24 hours to obtain Co1Mg3Al2Fe 0.1 -LDH catalyst precursor; the obtained product was washed, dried, ground, and then heated to 800°C at 5°C / min in a muffle furnace, calcined for 4 hours, and then cooled to room temperature at 10°C / min. Carbon dioxide oxidation ethane dehydrogenation reaction Weigh 0.1g of catalyst for reaction.

[0041] Example 4

[0042] A cobalt-iron dual-active-site synergistic catalyst (Co1Mg3Al2Fe 0.5 -MMO) preparation method, the specific steps are as follows:

[0043] First, a mixed solution of 0.01 mol / L cobalt nitrate, 0.01 mol / L magnesium nitrate, 0.01 mol / L iron nitrate and 0.01 mol / L aluminum nitrate was prepared with deionized water, and a mixed solution of 1.6 times the total molar amount of cations in sodium hydroxide and 2 times the molar amount of trivalent cations in sodium carbonate was prepared with deionized water; the two mixed solutions were transferred to a nucleation reactor and stirred for 5 minutes; the mixed solution was charged into a reactor and crystallized at 120°C for 24 hours to obtain Co1Mg3Al2Fe 0.5 -LDH catalyst precursor; the obtained product was washed, dried, ground, and then heated to 800°C at 5°C / min in a muffle furnace, calcined for 4 hours, and then cooled to room temperature at 10°C / min. Carbon dioxide oxidation ethane dehydrogenation reaction Weigh 0.1g of catalyst for reaction.

[0044] Figure 5 The performance comparison diagram of the catalysts obtained in Examples 1 to 4 of the present invention shows that Co1Mg3Al2-MMO, Co1Mg3Al2Fe 0.1 -MMO, Co1Mg3Al2Fe 0.2 -MMO, Co1Mg3Al2Fe 0.5 -MMO catalyst has good catalytic performance, Co1Mg3Al2Fe 0.2 -MMO catalyst has the best catalytic activity.

[0045] Principle of the present invention:

[0046] The present invention realizes high selectivity and high stability of carbon dioxide oxidation ethane dehydrogenation reaction (CO2-ODHE); the present invention combines the carbonate pyrolysis process with the ethane dehydrogenation reaction, and makes full use of the high calorific value CO2 in the carbonate pyrolysis industrial tail gas; cobalt nitrate hexahydrate, magnesium nitrate hexahydrate, aluminum nitrate nonahydrate and iron nitrate nonahydrate are used as raw materials, and Co with adjustable cobalt-iron ratio is prepared by nucleation crystallization isolation method x Mg3Al2Fe y -LDHs were used as catalyst precursors and further calcined to obtain a series of catalysts. Studies have shown that Co selectively breaks CH bonds and is the main active site for promoting ethane dehydrogenation, while the Fe site is responsible for the dissociation of carbon dioxide and supplements lattice oxygen to enhance the oxidative dehydrogenation of ethane. Under the synergistic catalysis of cobalt and iron dual active sites, it exhibits good catalytic activity and stability, thereby effectively solving the problem of low product selectivity in the reaction process, providing a new method for the efficient conversion of carbon dioxide, opening up new paths for carbon cycling and sustainable utilization of resources, and providing ideas for the design of innovative dehydrogenation catalysts.

[0047] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0048] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a cobalt-iron dual-active-site synergistic catalyst, characterized in that: The following steps are involved: (i) preparing a soluble metal salt mixed solution; (ii) preparing an alkaline solution; (iii) adding a soluble metal salt mixed solution and an alkaline solution into a nucleation reactor, and stirring the mixture to obtain a primary product; (iv) placing the initial product into a reaction vessel for crystallization, and washing, drying and grinding the crystallized product to obtain a cobalt-iron dual-active site synergistic catalyst precursor; (v) calcining the cobalt-iron dual-active-site synergistic catalyst precursor at high temperature to obtain the cobalt-iron dual-active-site synergistic catalyst.

2. The method for preparing the cobalt-iron dual-active-site synergistic catalyst according to claim 1, characterized in that: The solute of the soluble metal salt mixed solution includes soluble cobalt salt, soluble magnesium salt, soluble iron salt and soluble aluminum salt; the solvent of the soluble metal salt mixed solution is deionized water.

3. The method for preparing the cobalt-iron dual-active-site synergistic catalyst according to claim 1, characterized in that: The soluble metal salt mixed solution and the alkaline solution are both prepared by ultrasonic dispersion for 5 minutes to 30 minutes.

4. The method for preparing the cobalt-iron dual-active-site synergistic catalyst according to claim 2, characterized in that: The soluble cobalt salt is cobalt nitrate or cobalt chloride; the soluble magnesium salt is magnesium nitrate or magnesium chloride; the soluble iron salt is iron nitrate or iron chloride; the soluble aluminum salt is aluminum nitrate or aluminum chloride.

5. The method for preparing the cobalt-iron dual-active-site synergistic catalyst according to claim 2, characterized in that: The molar ratio of the soluble cobalt salt, the soluble magnesium salt, the soluble aluminum salt and the soluble iron salt is (0.5-2):3:2:(0.1-0.5), and the concentration of the soluble cobalt salt is 0.01-0.05 mol / L.

6. The method for preparing the cobalt-iron dual-active-site synergistic catalyst according to claim 1, characterized in that: The solute of the alkaline solution includes sodium hydroxide and sodium carbonate, and the solvent of the alkaline solution is deionized water.

7. The method for preparing the cobalt-iron dual-active-site synergistic catalyst according to claim 5, characterized in that: The molar amount of the sodium carbonate is 2 times the total molar amount of trivalent cations in the soluble metal salt mixed solution; the molar amount of the sodium hydroxide is 1.6 times the total molar amount of cations in the soluble metal salt mixed solution.

8. The method for preparing the cobalt-iron dual-active-site synergistic catalyst according to claim 1, characterized in that: The rotation speed of the nucleation stirring in step (iii) is 3000 rpm, and the stirring time is 5 minutes; the crystallization condition in step (iv) is crystallization at 120° C. for 24 hours; and the high-temperature calcination condition in step (v) is calcination at 800° C. for 4 hours in an air atmosphere.

9. A cobalt-iron dual-active-site synergistic catalyst prepared by the method according to any one of claims 1 to 8, characterized in that: The catalyst is Co1Mg3Al2-MMO, Co1Mg3Al2Fe 0.1 -MMO, Co1Mg3Al2Fe 0.2 -MMO or Co1Mg3Al2Fe 0.5 -MMO.

10. Use of a cobalt-iron dual-active-site synergistic catalyst prepared by the method of any one of claims 1 to 8 in carbonate pyrolysis CO2 coupled ethane oxidative dehydrogenation, characterized in that: The reaction conditions of carbonate pyrolysis CO2 coupled with ethane oxidative dehydrogenation are as follows: under normal pressure, a cobalt-iron dual-active site synergistic catalyst is filled in a continuous fixed bed reactor, and a reaction gas is introduced for reaction, wherein the reaction gas is composed of CO2, C2H6 and Ar, CO2 accounts for 5% of the total volume of the reaction gas, and C2H6 accounts for 5% of the total volume of the reaction gas; the reaction temperature is 600°C to 700°C, and the space velocity is 9000ml·g -1 ·h -1 .

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